The present invention relates generally to eddy current inspection and, more specifically, to eddy current probes for non-destructive testing of conductive materials.
Eddy current inspection is a commonly used technique for non-destructive testing of conductive materials for surface flaws. Eddy current inspection is based on the principle of electromagnetic induction, wherein a drive coil carrying currents induces eddy currents within a test specimen, by virtue of generating a primary magnetic field. The eddy currents so induced in turn generate a secondary magnetic field, which induces a potential difference in the sense coils, thereby generating signals, which may be further analyzed for flaw detection. In case of a flaw in the test specimen, as for example, a crack or a discontinuity, the eddy current flow within the test specimen alters, thereby altering the signals induced in the sense coils. This deviation in the signals may be used to indicate the flaws.
Existing systems, such as those described in commonly assigned U.S. Pat. No. 5,389,876, Hedengren et al, “Flexible Eddy Current Surface Measurement Array for Detecting Near Surface Flaws in a Conductive Part,” function on the above-mentioned principle. However, because magnetic fields are directional in nature, the eddy current probes described above are limited in their utility by the fact that a prior knowledge of crack orientation is required. This is also referred to as the directionality of eddy current probes.
Compensation for the directionality of conventional eddy current probes has been performed previously by repeatedly scanning a test specimen, with the eddy current probes being rotated slightly between each scan, in order to inspect the specimen for flaws along a number of orientations. However, this process is laborious and time consuming. Another possible approach would be to use an array probe designed to include number of elements formed on a substrate and slightly rotated. However, the latter arrangement would be inconvenient, in that it would either require a great deal of equipment or allow for a smaller scan.
Accordingly, there exists a need for an improved eddy current probe, array probe, and inspection system that overcomes the abovementioned problems inherent to compensating for the directionality of conventional eddy current probes.